FIELD OF THE INVENTION

The invention relates to a process for the preparation of a cheese product.

BACKGROUND TO THE INVENTION

The preparation of cheese by adding a coagulant and suitable starter material to a cheese milk to form a curd and whey followed by separation of curd and whey and processing the curd to a cheese product by, inter alia, molding, pressing and brining, is well known and widely applied. When separating the whey from the curd, small curd fines of typically up to 1 mm will inevitably be included in the whey stream. Such curd fines are often separated from the whey and processed into products such as cheese spread or animal feed.

However, other solutions for processing the separated whey stream containing the curd fines are known too. For example, NL 1024367 C2 discloses a process for the preparation of a cheese, wherein the curd fines in the whey stream are subjected to a treatment to decrease their size to a diameter of less than 250 pm, suitably less than 150 pm, so that they can form a stable suspension. This suspension is subsequently added to the cheese milk to be further processed into the cheese milk. It was found that by decreasing the size of the curd fines, these curd fines are indeed included in the final cheese product. This increases the efficiency of the process, as the curd fines now end up in the cheese product which has a higher value than cheese spread or animal feed.

EP 3539387 Al discloses a similar process in which the microbiological treatment of the starting cheese milk by means of bactofugation or filtration is integrated. More specifically, EP 3539387 Al discloses a process wherein the standardized cheese milk is subjected to a bactofugation or filtration treatment to produce a bactofugate (i.e. the concentrate of micro-organisms) and a treated cheese milk. The bactofugate is sterilized and re-combined with the treated cheese milk. To the resulting cheese milk a coagulant and/or starter material is added, thus forming a curd and whey. The curd and whey are separated and the curd is further processed into cheese. The whey stream contains curd fines and is subjected to a stabilization treatment to eventually obtain a stable suspension of curd fines which, in line with NL 1024367 C2, suitably have a diameter of less than 250 pm, more suitably less than 150 pm. This suspension is then added to the bactofugate before or after sterilization, but anyhow before addition to the treated cheese milk.

The present invention aims to further enhance the efficiency of the cheese making process by optimizing the re-use and recycling of process streams in a cheese making process. Furthermore, the present invention aims to provide a cheese making process that results in a high quality cheese end product having an excellent taste, microbiological quality and shelf-life.

SUMMARY OF THE INVENTION

The present invention relates to a process for the preparation of cheese, wherein not only the curd fines and bactofugate are re-used in the cheese production process, but wherein also the whey cream and possibly one or more other process streams are re-used in an integrated way. This makes the cheese production process highly efficient and further improves valorisation of the original starting milk.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the present invention relates to a process for the preparation of cheese comprising the steps of a) preparing a standardized cheese milk by subjecting a starting milk to a standardization treatment; b) subjecting the standardized cheese milk to a pasteurization treatment to obtain pasteurized cheese milk; c) coagulating the pasteurized cheese milk to obtain a coagulated cheese milk; d) separating the coagulated cheese milk into curd and whey; and e) processing the curd into cheese, wherein (i) the standardization treatment comprises a bactofugation treatment, wherein a bactofugate is obtained;

(ii) the whey is subjected to a whey clarification treatment to obtain clarified whey and whey comprising curd fines;

(iii) the whey comprising curd fines is subjected to a stabilization treatment to obtain a processed curd fines suspension;

(iv) the clarified whey is subjected to a fat separation treatment to obtain low fat clarified whey and whey cream;

(v) the processed curd fines suspension, the whey cream and the bactofugate are subjected to a sterilization treatment; and

(vi) the sterilized curd fines suspension, the sterilized whey cream and the sterilized bactofugate obtained in step (v) are added to the standardized cheese milk before the standardized cheese milk is subjected to the pasteurization treatment in step b).

In step a) a standardized cheese milk is prepared. The starting milk for preparing the standardized milk will typically be raw milk and can be cow’s milk, goat milk or any other milk used for cheese making. Cow’s milk and goat milk are, however, preferred. The actual preparation of the standardized cheese milk can be achieved in the usual ways known in the art. Standardization of milk is a well- known way to ensure the milk is microbiologically treated, that is, potentially harmful micro-organisms are removed in order to ensure a safe end-product that is of good and reliable quality and has a sufficiently long shelf-life. Furthermore, standardization may also involve adjusting the fat content of the cheese milk, sometimes also protein and/or lactose content, and bringing this to the desired level. The desired level will ultimately be determined by the type of cheese to be produced and the desired fat content of the cheese.

For the purpose of the present invention the standardization treatment in step a) anyhow comprises a bactofugation treatment. Bactofugation is a well- known anti-microbiological treatment to reduce the number of spores of bacteria, such as Clostridium tyrobutyricum, in the cheese milk. Bactofugation is a centrifugation treatment in which the bacteria and bacteria spores to be removed end up in the sediment (bactofugate) whilst the supernatant is further processed into the standardized cheese milk. Bactofugation usually takes place at elevated temperature, that is, at a temperature between 45 and 65 °C, suitably between 50 and 60 °C. The bactofugate should be treated carefully, as it contains a high concentration of bacteria and bacteria spores at elevated temperature. The bactofugate will usually also have a high protein content which makes it useful as a recycle stream. Therefore, the bactofugate is subjected to a sterilization treatment to avoid rapid bacteria growth in the bactofugate and to enable recycling.

The standardization may also comprise a thermization treatment. Such thermization treatment may take place either before or after the bactofugation treatment. Accordingly, in the process of the present invention thermization may be applied to the starting milk or to the treated milk from the bactofugation step, if bactofugation takes place first. Thermization is a well-known step and is commonly applied to a milk stream that is intended to be held after intake for extended periods of refrigerated storage before further processing, such as the production of cheese. It is usually less severe than pasteurization and typically involves heating at a temperature in the range of 55 to 70 °C for 9-30 seconds, suitably in the range of 60 to 68 °C for 9-20 seconds, although longer times are also sometimes used. For the purpose of the present invention it is preferred to include a thermization step in the standardization.

The standardization treatment may further comprise a fat separation treatment before or after the bactofugation treatment to obtain low fat milk and cream. Such fat separation treatment is typically also a centrifugal separation step, with the cream being recovered as sediment and the defatted milk as the supernatant. Fat separation is a commonly applied treatment and suitable fat separation devices are well known. If the standardization includes such fat separation treatment, then the standardization may further comprise a fat adjustment step wherein a fat source is added to the low fat treated milk in order adjust the fat content of the cheese milk as will be described in more detail below.

An advantage of subjecting the starting milk to a fat separation treatment before bactofugation is that smaller bactofugation equipment is needed to perform the bactofugation treatment as part of the starting milk has already been separated as cream before the low fat milk resulting from the fat separation is subjected to bactofugation. In this case the cream needs an additional anti- microbiological treatment during its further processing, typically a pasteurization treatment. When subjecting the starting milk first to bactofugation and subsequently subjecting the treated milk from the bactofugation to a fat separation treatment the reverse is true: a cleaner cream is obtained, but larger bactofugation equipment is needed. Both embodiments are equally suitable.

If the standardization comprises both a fat separation treatment and a thermization treatment it is preferred that the starting milk is first subjected to fat separation and bactofugation, irrespective of the order in which these treatments take place, and the resulting low fat, treated milk stream is subsequently subjected to thermization as described above. Fat content of the resulting thermized milk stream will be low and if a higher fat content is desired, a fat source should be added to adjust the fat content to the desired level. This fat source will usually be derived from one or more fat-containing streams that form part of the same cheese producing process. In a preferred embodiment, accordingly, the fat source is selected from full fat milk, cream, whey cream and a combination of two or more of these fat sources.

Cream can be obtained by a fat separation treatment as described above, whilst whey cream is obtained by subjecting clarified whey resulting from step (ii) to a fat separation treatment in step (iv) as will be described in more detail hereinafter.

Full fat milk is suitably prepared in a separate line by a similar standardization treatment as described above, but excluding the fat separation treatment. Accordingly, when producing such full fat milk the starting raw milk is subjected to a bactofugation treatment, optionally followed or preceded by a thermization treatment as described above. The resulting full fat milk can suitably be combined with the low fat milk to obtain the standardized cheese milk. The desired fat content of this standardized cheese milk is determined by the type of cheese to be produced and the desired fat content of the cheese to be produced. For example, when producing a 10+ cheese the cheese milk should be standardized to a much lower fat content than when aiming to produce a 48+ cheese. If the standardization includes a fat separation treatment and hence the production of a low fat milk stream as well as a subsequent fat adjustment step by adding full fat milk as the fat source, then the bactofugate obtained by producing the full fat milk is suitably also to be re-used in the process of the present invention. This is preferably achieved by combining both bactofugates (i.e. the bactofugate resulting from production of the low fat milk stream and the bactofugate resulting from production of the high fat milk stream) into a single bactofugate that is further processed in accordance with the present invention.

Combining the high fat milk stream and low fat milk stream can, for example, be effected by passing both streams in the desired quantities into a standardization tank where they are mixed in such ratio that the resulting standardized cheese milk has the desired fat content. From this tank the standardized cheese milk is then further processed. In another embodiment the low fat milk stream and the high fat milk stream are passed into separate buffer tanks. From these buffer tanks the streams can subsequently be dosed in the desired ratio into a dosing tank, pipeline or the cheese vat to form the standardized cheese milk by using dosing systems known in the art.

If the standardization includes a fat separation treatment and hence the production of a low fat milk stream as well as the adjustment of fat content by adding full fat cheese milk as the fat source, then the bactofugate obtained by producing the full fat cheese milk is suitably also re-used in the process of the present invention in the same way as the bactofugate obtained when producing the low fat milk. This is preferably achieved by combining both bactofugates into a single bactofugate that is further processed in accordance with the present invention.

In a preferred embodiment the standardization treatment comprises the steps of al) subjecting the starting milk to a fat separation treatment, thus obtaining low fat milk and cream; a2) subjecting the low fat milk to a bactofugation treatment, thus obtaining a bactofugate and a treated low fat milk; a3) subjecting the treated low fat milk to a thermization treatment, thereby obtaining a low fat thermized milk; a4) adjusting the fat content of the low fat thermized milk by adding a suitable fat source, thereby obtaining the standardized cheese milk.

The fat source used in step a4) preferably is obtained by subjecting the same type of starting milk to a treatment comprising the steps of a2’) subjecting the starting milk to a bactofugation treatment, thus obtaining a bactofugate and a treated full fat milk; and a3’) subjecting the treated full fat milk to a thermization treatment, thereby obtaining the full fat milk used as fat source in fat content adjusting step a4).

The bactofugates obtained in steps a2) and a2’) are suitably combined into a single bactofugate stream for further processing in the process of the present invention, more specifically from step (v) onwards. They could, however, also be separately processed in the process of the present invention.

In another preferred embodiment the standardization treatment comprises the steps of al) subjecting the starting milk to a bactofugation treatment, thus obtaining a bactofugate and a treated milk; a2) subjecting the treated milk to a fat separation treatment, thus obtaining a treated low fat milk and cream; a3) subjecting the treated low fat milk to a thermization treatment, thereby obtaining a low fat thermized milk; a4) adjusting the fat content of the low fat thermized milk by adding a suitable fat source, thereby obtaining the standardized cheese milk.

The fat source used in step a4) preferably is obtained by subjecting the same type of starting milk to a treatment comprising the steps of al’) subjecting the starting milk to a bactofugation treatment, thus obtaining a bactofugate and a treated full fat milk; and a3’) subjecting the treated full fat milk to a thermization treatment, thereby obtaining the full fat milk used as fat source in fat content adjusting step a4).

The bactofugates obtained in steps a2) and al’) are suitably combined into a single bactofugate stream for further processing in the process of the present invention, more specifically from step (v) onwards. They could, however, also be separately processed in the process of the present invention.

In yet another preferred embodiment the standardization consists of steps al) to a3) of any of the above two embodiments, wherein the low fat thermized milk is further processed as the standardized cheese milk, thus eventually obtaining low fat cheese.

In an alternative embodiment, the starting milk is first subjected to bactofugation, thus producing a bactofugate and a treated milk stream. Part of this treated milk stream is subsequently subjected to a fat separation treatment and the remaining part is not. Both the resulting low fat milk stream and full fat milk stream are then separately thermized and re-combined in the desired ratio, either in a standardization tank or via separate buffer tanks, to obtain a standardized cheese milk of the desired fat content.

In step b) the standardized cheese milk is pasteurized, thus yielding a pasteurized cheese milk. Pasteurization is a well-known treatment and will typically involve heating the standardized cheese milk to a temperature in the range of 70 to 80 °C for 10-60 seconds, more suitably in the range of 71 to 75 °C for 10-20 seconds.

In step c) the pasteurized cheese milk is coagulated. Coagulation is essentially the formation of a gel by destabilizing the casein micelles causing them to aggregate and form a network which partially immobilizes the water and traps the fat globules in the newly formed matrix. As is well known in the art, coagulation can be accomplished in various ways, e.g. with an acid treatment or by adding a coagulant (an enzyme). One or more starters are usually also added. In general, a starter is a culture of one or more species or strains of lactic acid bacteria added to the treated cheese milk to start fermentation of the cheese milk. Each starter has a characteristic proteolytic system, which is important for the ripening of the cheese, as it determines how the proteins are hydrolyzed and how the peptides formed as result of such hydrolyzation are converted into amino acids and flavor compounds. In addition, the starter impacts the texture of the cheese and the possible formation of ‘eyes’ in the cheese caused by bubbles of carbon dioxide that can be produced by certain starter cultures. Accordingly, each cheese type has its own, characteristic starters. Starters may be added in broadly varying amounts, typically from 1 to 1000 grams per 100 liters of pasteurized cheese milk.

Coagulation by adding a coagulation-inducing enzyme or coagulant is most frequently applied in cheese making. Chymosin, also known as rennin or rennet, is widely used for enzyme coagulation. In the past chymosin was extracted from dried calf stomachs for this purpose, but the cheese making industry has expanded beyond the supply of available calf stomachs. It turns out that many proteases are able to coagulate milk by converting casein to para-casein and alternatives to chymosin are readily available. "Rennet" now is the name given to any enzymatic preparation that clots milk. The major component of rennet is chymosin but in commercial preparations of rennet other proteases, typically bovine pepsin, are found too in varying concentrations. So when using the term “rennet” in this application reference is made to such enzymatic preparation. Rennet is typically added in an amount ranging from 2 to 25 grams of rennet per 100 liters of pasteurized cheese milk.

In order to further promote the coagulation calcium chloride may be added to the pasteurized cheese milk. This is well known and commonly applied in cheese making. The calcium chloride is typically added as an aqueous solution in concentrations ranging from 10 to 40% by weight. The amount of calcium chloride added may vary within wide limits and will generally be in the range of 1 to 100 grams of calcium chloride per 100 liters of cheese milk.

Accordingly, in a preferred embodiment coagulation step c) is carried out by adding a coagulant, suitably rennet, and one or more starters to the pasteurized cheese milk resulting from step b) and allowing the pasteurized cheese milk to coagulate to obtain a coagulated cheese milk.

In step d) the coagulated cheese milk is separated into curd and whey. Such separation can take place by conventional separation means known in the art of cheese making. A commonly applied separating method is cutting the curd formed and draining a substantial part of the whey that was originally contained in the gel matrix of the curd and is released as a result of cutting the curd. Such draining can take place in one or more steps, involving suction and a draining column with intermediate washing of the curd mass with warm water. This is all common practice in cheese making and well known. If multiple steps are used to remove the whey, the different whey streams thus obtained are suitably combined into a single whey stream for further processing in the process of the present invention.

In step e) the cut curd obtained in step d) is further processed into cheese in the conventional way. Such further processing will typically comprise scalding, stirring, at least one further step for separating any remaining whey from the curd (typically by draining), molding, pressing, brining, washing, drying, coating or foil packaging the cheese and allowing the cheese to further ripen. These steps are all well known. Any whey recovered from any further curd/whey separation step(s) could either be combined with the main whey stream obtained in step d) or be separately processed into a different product.

Following the main steps described above the different streams are further processed in accordance with the present invention. The whey obtained in step d) is subjected to a whey clarification treatment to obtain clarified whey and whey comprising curd fines in step (ii). Such whey clarification treatment can be carried out by ways known in the art and will suitably comprise a centrifugal treatment resulting in the whey stream comprising the curd fines as the sediment and the clarified whey the supernatant. Suitable whey centrifuges that can be used for this purpose are commercially available. Whey clarification by means of filtration or sieving could be an alternative way to separate curd fines from the whey, thereby obtaining a clarified whey and a whey stream comprising the curd fines. Suitable filters include self-cleaning automatic filters.

The resulting whey stream comprising curd fines contains finely dispersed curd fines that may have a diameter of up to 1 mm. This stream needs to be stabilized first before it can be recycled. Such stabilization takes place in step (iii) and will involve reducing the size of the curd fines. Ways to reduce particle size and form a stable suspension are described in NL 1024367 C2 and EP 3539387 Al, both discussed above. In a preferred embodiment step (iii) comprises a homogenization treatment to obtain the stable, processed curd fines suspension. Such homogenization treatment could be effected by ways known the art, such as by using one or more homogenizers. Such homogenizers are commercially available. For the processed curd fines suspension to be stable, the curd fines in the suspension suitably have a particle size below 250 pm, preferably below 150 pm, more preferably in the range of 10 to 100 pm. Particle size, as referred herein, means volume weighted mean size (or volume mean size) and can be determined by laser diffraction. Suitable laser diffraction equipment is known in the art and includes, for example, Malvern Mastersizer equipment of Malvern Pananalytical. Concentration of the suspended particles in the processed curd fines suspension suitably is in the range of 1 to 10% by weight, based on total weight of the suspension.

It was found that particularly good results are obtained if the processed curd fines suspension has a pH of at least 6.5. The pH of the other two recycle streams (i.e. bactofugate and whey cream) will usually have a pH above 6.5, so that, when these streams would be mixed with the processed curd fines suspension into a single recycle stream, the processed curd fines suspension would be the stream causing the pH of the single recycle stream to possibly drop below 6.5. Accordingly, the pH of the processed curd fines suspension is suitably controlled to be at least 6.5, preferably in the range of 6.5 to 7.6, more preferably 6.5 to 7.3 and most preferably 6.6 to 7.1. Such control could comprise simply checking the pH of the processed curd fines suspension not to drop below 6.5, but could also comprise actively adjusting the pH to the desired level as will be described in more detail below.

It was found that a pH value of at least 6.5 ensures an adequate heat stability not only of the processed curd fines suspension, but also of any recycle mix stream comprising the bactofugate, whey cream and processed curd fines suspension. More specifically, such pH helps to stabilize the suspension or recycle mix stream by ensuring that any casein present therein will not flocculate and remains stably dissolved when the processed curd fines suspension or recycle mix stream is heated later in the process, notably upon sterilization in step (v). By preventing flocculation of the casein upon heating any clogging of pipelines and equipment, in particular the sterilizer, is prevented. This is particularly relevant for the recycle mix stream, as this stream comprises the bactofugate which is relatively rich in casein in comparison with the processed curd fines suspension. Accordingly, if the processed curd fines suspension has a pH below 6.5, this pH is suitably adjusted to a value of at least 6.5 and preferably to a value in the ranges indicated above, in particular in an embodiment wherein the processed curd fines suspension, whey cream and bactofugate are mixed into a single recycle stream before sterilization in step (v). Such adjustment of the pH can be attained by adding an aqueous base solution, such as an aqueous sodium hydroxide solution, to either the whey comprising curd fines (i.e. prior to the stabilization treatment) or to the processed curd fines suspension (i.e. after the stabilization treatment). Adjusting the pH of the whey comprising curd fines by adding an aqueous base solution thereto is preferred. If processed curd fines, whey cream and bactofugate are mixed into a single recycle stream prior to sterilization, this single recycle stream should have a pH in the same range as indicated above for the processed curd fines suspension. Accordingly, in a preferred embodiment the pH of the processed curd fines suspension is controlled to be at least 6.5, preferably in the range of 6.5 to 7.6, more preferably 6.5 to 7.3 and most preferably 6.6 to 7.1, by adjusting the pH of the whey comprising curd fines to such value, preferably by adding an aqueous base solution to the whey comprising curd fines prior to being subjected to the stabilization treatment in step (iii). For example, if the stabilization treatment comprises a homogenization, the aqueous base solution can be mixed into the whey stream that comprises the curd fines to obtain the desired pH after which the resulting pH-stabilized stream is passed into the homogenizer to form the processed curd fines suspension that is sterilized and recycled to the standardized cheese milk.

The other stream resulting from step (ii), the clarified whey, is subjected to a fat separation treatment to obtain low fat clarified whey and whey cream in step (iv). Such fat separation treatment is suitably also a centrifugal treatment and can be carried out by ways known in the art using commercially available equipment. The low fat clarified whey can be used for many different application, for example as a source of different ingredients, such as whey protein isolate (WPI), whey protein concentrate (WPG), lactalbumin, immunoglobulins, lactose, minerals and demineralized whey. One of the key integration features of the present invention is that in step (v) the whey cream obtained in step (iv), the processed curd fines suspension resulting from step (iii) and the bactofugate obtained in step a) are all subjected to a sterilization treatment. In step (vi) the resulting sterilized whey cream, sterilized processed curd fines suspension and sterilized bactofugate are then added to the standardized cheese milk obtained in step a) before pasteurization step b), thereby enabling further processing of these streams into cheese. Combining the different process streams in this way and integrating them into the cheese production process ensures an optimum use of all components from the original starting milk, so that they end up in a high value cheese instead of being processed into lower value products, such as cheese spread or animal feed.

This integration of the different process streams can be effected in different ways. In one suitable embodiment the processed curd fines suspension obtained in step (iii) is first combined with the whey cream obtained in step (iv) into a single stream before being subjected to sterilization in step (v). Temperatures of the whey cream and curd fines suspension will typically be similar, that is, in the range of 25 to 45 °C, suitably 30 to 40 °C, so combining them will not require specific heating, cooling or mixing equipment. When combining these streams into a single stream, the single stream may be stored in one or more buffer tanks before passing it into the sterilizer to enable storage as well as effective dosing into the sterilizer. This buffer tank may be kept at any temperature between 5 and 80 °C, depending on factors, such as residence time of the recycle stream in the buffer tank and type and capacity of sterilizing equipment used. At longer residence times cold storage would be preferred (that is, temperature is kept relatively low, e.g. at 5-15 °C), whilst at short residence times a higher storage temperature may be feasible (e.g. 65-80 °C).

In another suitable embodiment the processed curd fines suspension and whey cream, either separately or combined into a single stream as described above, are first combined with the bactofugate into a single recycle stream which is subsequently subjected to sterilization in step (v). An advantage of this embodiment is that the sterilization can be carried out in a single sterilizer, as only one stream needs to be sterilized. Since the bactofugate will typically have a higher temperature than the whey cream and curd fines suspension, mixing of the streams is suitably carried out such that the resulting single recycle stream will have a uniform temperature before being subjected to the sterilization treatment in step (v). More specifically, the bactofugate will typically have a temperature in the range of 50 to 65 °C, whilst the temperature of the whey cream and curd fines suspension will commonly be in the range of 25 to 45 °C, suitable 30 to 40 °C. One suitable way of effectively mixing the three streams is to pass the three streams separately into a single pipeline system which is kept at a constant temperature that should be high enough to prevent too rapid growth of the bacteria in the bactofugate, but at the same time should be well below sterilization temperature and at a temperature that from both a process economics and safety perspective is good to handle. Accordingly, it was found that mixing the three aforesaid streams between steps (iii) and (iv) could suitably be effected by passing each stream separately into a pipeline that is kept at a constant temperature in the range of 65 to 90 °C, preferably 70 to 85 °C. Instead of passing each stream separately into the aforesaid pipeline it is also possible to first combine the processed curd fines suspension and whey cream into a single stream and then pass this single stream and the bactofugate separately into this pipeline. This pipeline can then feed the mixture to the sterilization treatment, possibly via a buffer tank kept at a similar temperature in the range of 65 to 90 °C, preferably 70 to 85 °C. Alternatively, the streams are passed into a mixing tank which is kept at a constant temperature in the range of 65 to 90 °C, preferably 70 to 85 °C, and the single recycle stream is then passed from this mixing tank to the sterilization treatment. The single recycle stream could also be sterilized in this mixing tank by increasing the temperature of the single recycle stream in the mixing tank to a temperature between 90 and 100 °C and maintaining the mixing tank at this temperature for 30 to 50 minutes, for example 40-45 minutes at 95 °C, whilst continuously stirring.

In general, whenever buffer tanks are used, it is preferred that continuous stirring takes place in the buffer tank to ensure the composition and temperature of its contents remain homogenous.

In step (v) the processed curd fines, whey cream and bactofugate, either separately or combined into a single recycle stream or in another combination as described above, are subjected to a sterilization treatment. Sterilization treatment can take place by ways known in the art. Suitable sterilization devices are commercially available. Examples of suitable sterilizers that are commonly used in the dairy industry are tube sterilizers (monotube, multitube, helical tube etc.). Sterilization typically takes place by subjecting the flowing process stream(s) to a temperature in the range of 90 to 135 °C for a period ranging from 3 seconds to 5 minutes. In general, the lower the temperature, the longer the sterilization time. For example, an ultra-high temperature treatment at 135 °C could be as short as 3-6 seconds, whereas a sterilization treatment at 115 °C may take 2-3 minutes and a sterilization at 95 °C may take between 30 to 50 minutes. Furthermore, a combination of different temperatures and residence times is also possible, such as 1-3 minutes at 95 °C followed by 10-20 seconds at 125 °C. For the purpose of the present invention a particular suitable sterilization treatment would be subjecting the single recycle stream to a temperature of 90 to 105 °C for 1.5 to 3 minutes followed by 120 to 130 °C for 10 to 20 seconds.

After the sterilization treatment the sterilized curd fines suspension, sterilized whey cream and sterilized bactofugate are added to the standardized cheese milk obtained in step a) before the standardized cheese milk is subjected to the pasteurization treatment in step b). Again, depending on how the different process streams entered the sterilizer, these sterilized streams will either leave the sterilizer as a single sterilized stream which is added to the standardized cheese milk or as two or more separate sterilized streams which are added to the standardized cheese milk. In the latter case, these streams may either first be combined before being added to the standardized cheese milk or be added separately to the standardized cheese milk. The key feature is that they are combined with the standardized cheese milk, so that they are further processed into cheese via subsequent process steps c) to e).

Apart from the whey cream, curd fines suspension and bactofugate the process of the present invention also allows for other process streams to be recycled and be further processed into cheese by combining them with the standardized cheese milk, thereby further improving efficiency of the process and valorisation of the starting milk. Accordingly, if the process of the present invention includes a fat separation step as part of the standardization treatment in step a) which is a centrifugal separation treatment, this fat separation step also yields a centrifuge sludge in addition to the cream and low fat milk. This centrifuge sludge could then suitably be combined with the bactofugate and this combined stream could then be further processed as described hereinbefore for the bactofugate, thereby becoming part of the process streams that are recycled.

In yet another suitable embodiment the cream obtained in the fat separation treatment is first subjected to a pasteurization treatment and then stored in a storage tank. The storage tank will be regularly emptied and the pasteurized cream removed from the storage tank is then further processed. The storage tank is subsequently flushed with water to remove any pasteurized cream that has remained behind in the tank, so that the storage tank can be filled with a new batch of pasteurized cream. The flushing water that leaves the tank will, therefore, contain the pasteurized cream that had remained behind; this stream is accordingly referred to as “flushed cream”. This flushed cream could then also be subjected to the sterilization treatment in step (v). Accordingly, in this embodiment the cream is subjected to a treatment comprising the steps of aal) pasteurization; aa2) storing the pasteurized cream thus obtained in a storage tank; aa3) removing the pasteurized cream from the storage tank for further processing; aa4) flushing the storage tank with water, thereby obtaining flushed cream; and aa5) subjecting the flushed cream to the sterilization treatment in step (v).

To effectuate the above step aa5), the flushed cream could first be combined with one or more of the other streams that are sterilized in step (v) or, alternatively, be passed directly into the sterilizer. For example, the flushed cream could be passed into one or more of the buffer tanks, in which bactofugate or the whey cream/curd fines suspension is stored before being passed to the sterilizer.

Finally, in step (vi) the sterilized curd fines suspension, the sterilized whey cream and the sterilized bactofugate are added to the standardized cheese milk obtained in step a) before the standardized cheese milk is subjected to the pasteurization treatment in step b). When sterilized separately, these streams can also be added separately to the standardized cheese milk. Alternatively, they are combined after sterilization and subsequently added to the standardized cheese milk. In the embodiment where the processed curd fines suspension, the whey cream and the bactofugate are combined before sterilization and the resulting single recycle stream is sterilized, suitably via storage in a buffer tank, the sterilized single recycle stream is added to the standardized cheese milk before pasteurization in step b). By recycling and integrating all these different process streams into the cheese making process, an optimum use of all components from the original cheese milk is achieved by ensuring these components end up in the high value cheese instead of being processed into lower value products such as cheese spread or animal feed.

FIGURES

Figure 1 is a schematic representation of the process of the present invention, wherein bactofugate, processed curd fines and whey cream are fed separately to a sterilizer.

Figure 2 is a schematic representation of the process of the present invention, wherein standardization also includes a thermization and fat separation treatment and fat content of the standardized cheese milk is adjusted. The schematic representation in Figure 2 also shows the embodiment in which centrifuge sludge is combined with the bactofugate before sterilization.

Figure 3 is a schematic representation of the process of the present invention, wherein flushed cream is recycled to the buffer tank of bactofugate and to the buffer tank of the mixture of processed curd fines and whey cream before sterilization.

Figure 4 is a schematic representation of the process of the present invention, wherein bactofugate, processed curd fines and whey cream are added to a circular line and combined into a single recycle stream kept at a higher temperature. This circular line is connected with a buffer tank from which the single recycle stream is passed to the sterilization treatment. The figures are schematic representations and hence do not show all equipment used in the actual process. For example, buffer tanks, dosing tanks, pumps, heat exchangers, dosing points and the like may not be shown, but it will be appreciated by those skilled in the art that such ancillary equipment may be used as well.

In Figure 1 the raw milk 2 is passed from raw milk tank (1) and subjected to bactofugation treatment (3) resulting in treated milk (4) which is passed into standardized cheese milk tank (8), and bactofugate (5). Bactofugate (5) is subjected to sterilization treatment (6a) in sterilization section (6) and the resulting sterilized bactofugate (7a) is combined into a sterilized stream (7) and passed into standardized cheese milk tank (8). Standardized cheese milk (9) is subjected to a pasteurization treatment (10) before the pasteurized, standardized cheese milk (11) is coagulated (12) and the resulting coagulated cheese milk (13) is subjected to a separation treatment (14) resulting in a curd (15) and whey stream (18). The curd (15) is further processed (16) into cheese (17), while the whey (18) is subjected to whey clarification treatment (19) resulting in a whey comprising curd fines (20) and clarified whey (23). The whey comprising curd fines (20) is subjected to stabilization treatment (21) resulting in processed curd fines suspension (22). This processed curd fines suspension (22) is subjected to a sterilization treatment (6c) in sterilization section (6), thereby obtaining sterilized curd fines suspension (7c) which is combined into sterilized stream (7) and passed into standardized cheese milk tank (8). The clarified whey (23) is subjected to fat separation treatment (24), thereby obtaining defatted clarified whey (26) and whey cream (25). This whey cream (25) is subjected to a sterilization treatment (6b) in sterilization section (6), thereby obtaining sterilized whey cream (7c) which is combined into sterilized stream (7) and passed into standardized cheese milk tank (8). Accordingly, in this way the sterilized bactofugate (7a), the sterilized whey cream (7b) and the sterilized curd fines suspension (7c) are fed back to the standardized cheese milk and hence are further processed into cheese (17).

In Figure 2 part of the raw milk (2) is subjected to a fat separation treatment (27) resulting in cream (28) and a low fat milk (2a). If the fat separation treatment (27) is a centrifugal treatment, then also a centrifugal sludge (30) will be produced. This low fat milk (2a) is subjected to bactofugation treatment (3) resulting in bactofugate (5b) and treated low fat milk (4a) which is subjected to thermization treatment (29). The resulting low fat thermized milk (4b) is passed into standard cheese milk tank (8). Another part of raw milk (2) is subjected directly to bactofugation treatment (3) resulting to a bactofugate (5a) and a treated full fat milk (4c). The bactofugates (5a) and (5b) are combined into a single bactofugate (5c) which is subjected to sterilization treatment (6a) in sterilization section (6). The treated full fat milk (4c) is subjected to thermization treatment (29) resulting in thermized full fat milk (4d) which is used as fat source to adjust the fat content of the cheese milk in standardized cheese milk tank (8). Further processing of standardized cheese milk (9) and addition of sterilized stream (7) to the standardized cheese milk in standardized cheese milk tank (8) are the same as in Figure 1. Figure 2 also shows the option of combining all or part of centrifuge sludge (30) resulting from fat separation treatment (27) with bactofugate (5).

In Figure 3 cream (28) is subjected to pasteurization (31) and stored in tank (33). Pasteurized cream (34) can be withdrawn from this tank for further processing or use. When tank (33) is empty, it flushed resulting in flushed cream (35). Cold buffer tank (37) is used to store bactofugate (5), while cold buffer tank (39) is sued to store processed curd fines suspension (22) and whey cream (25). Flushed cream (35) can be passed into one or both of the cold buffer tanks (37) and (39). Combined bactofugate/flushed cream (38) from buffer tank (37) and combined processed curd fines suspension/whey cream/flushed cream (40) from buffer tank (39), are then passed into sterilization section (6) where they are subjected to sterilization treatments (6a) and (6b), respectively. Resulting sterilized streams (7a) and (7b) are combined into sterilized stream (7) and fed into standardized cheese milk tank 8 for further processing. Such further processing can then take place as shown in Figure 1.

In Figure 4 bactofugate (5), processed curd fines (22) and whey cream (25) are all fed into circular line (42) which is kept at a continuously high temperature (65 to 90 °C, preferably 70 to 85 °C, as described above) and feeds the mixed recycle stream in circular line (42) into hot buffer tank (41). From this hot buffer tank (41) single recycle stream (43) is passed into sterilization section (6) for sterilization and sterilized, single recycle stream (7) is passed into standardized cheese milk tank (8) for further processing. Such further processing can then take place as shown in Figure 1.

EXAMPLES

Example 1 - Preparation of 48+ Gouda cheese

Raw milk was heated to 55 °C and subjected to a fat separation treatment in a cream separator. The resulting skimmed milk was subjected to a bactofugation treatment at 56 °C, thus yielding a bactofugate (bactofugate 1) and treated skimmed milk. The treated skimmed milk was thermized for 10 seconds at 63 °C and the thermized skimmed milk was passed into a standardization tank which was kept at 6 °C.

Another part of the same raw milk was subjected to a bactofugation treatment at 56 °C, thus also yielding a bactofugate (bactofugate 2) and a treated full fat milk. The treated full fat milk was thermized for 10 seconds at 63 °C and the thermized full fat milk stream was dosed into the same standardization tank together with the sterilized mix stream (as described below), so that the fat content of the standardized cheese milk in the standardization tank was 1.09 times higher than the protein mass concentration of the cheese milk to prepare the cheese milk of a 48+ Gouda type cheese.

Cheese milk recipe and cheese milk composition are indicated in Table 1 and Table 2, respectively.

Table 1 - Cheese milk recipe Table 2 - Cheese milk composition ^x > as determined by Foss Milkoscan FT2 (IR)

Bactofugates 1 and 2 were combined into a single bactofugate stream. This bactofugate stream was passed into a circular pipeline which was continuously kept at 75 °C.

The standardized cheese milk was meanwhile pasteurized for 15 seconds at 72 °C, the pasteurized cheese milk thus obtained was cooled and then passed into a cheese vat for coagulation. Starter culture, calcium chloride and coagulant were added and a curd was allowed to form at 30 °C during 30 minutes. The curd was subsequently cut, so that whey was released from the gel network. The whey was removed through a sieve by suction and contained curd fines of up to 1 mm in diameter (first whey). After the first whey was removed from the cut curd, warm washing water was added to the remaining curd mass under continuous stirring so that the temperature of the curd mass in the cheese vat increased to approximately 33 °C. Stirring continued for 20 minutes. The curd mass was subsequently pumped into a buffer tank from it was passed into a draining column where further whey was drained from the curd mass (second whey). This second whey was combined with the first whey into a single whey stream. This whey stream was then cleaned by passing it through a whey clarification centrifuge operated at approximately 33 °C, resulting in a clarified whey and a whey stream comprising curd fines. This whey stream comprising curd fines having a temperature of approximately 33 °C was passed into a two-stage homogenizer, where the curd fines were homogenized at successively 350 bar and 50 bar resulting in a stable processed curd fines suspension with a particle size distribution (as determined by laser diffraction using a Malvern Mastersizer 2000) of 98 vol% < 250 pm and 95 vol% < 150 pm with a mean particle size of 70 pm. The processed curd fines stream was subsequently passed into the same circular pipeline as the bactofugate.

The clarified whey obtained from the whey clarification centrifuge was fed into a whey decreaming centrifuge operated at approximately 33 °C, resulting in whey cream and defatted clarified whey. The whey cream was subsequently passed into the same circular pipeline as the bactofugate and processed curd fines stream.

Bactofugate, processed curd fines and whey cream were, accordingly, dosed into the circular pipeline that was kept at 75 °C. The resulting circular mix stream had a pH of 6.7 and was passed into a continuously stirred, hot buffer tank which was also kept at 75 °C. It took 8 hours to completely fill the hot buffer tank. The hot buffer tank was subsequently emptied within 2 hours by feeding the mix stream from the hot buffer tank into a monotube sterilizer, where it was sterilized by keeping the mix stream at 95 °C for 2 minutes followed by 125 °C for 15 seconds. The sterilized mix stream was subsequently rapidly cooled to 6 °C and passed into a dosing tank kept at 6 °C. From this dosing tank the sterilized mix stream was fed to the standardization tank referred to above, from which the standardized cheese milk was further processed as described above.

After removal of the second whey the curd leaving the draining column at the bottom is cut and the resulting cylindrically shaped curd blocks are put into round pressing vats in which they are pressed into wheel-shaped cheeses of 12,5 kg. The cheeses were subsequently further processed into the final cheese product by brining, coating and ripening the cheese.

By using this process it was found that bactofugate, curd fines and whey cream could be effectively recycled, thereby optimizing the use of these streams in producing cheese.

Example 2 - Preparation of 48+ Gouda cheese

Raw milk was heated to 55 °C and subjected to a fat separation treatment in a cream separator. The resulting skimmed milk was subjected to a bactofugation treatment at 56 °C by two centrifuges in series, thus yielding a bactofugate (bactofugate 1) and treated skimmed milk. The treated skimmed milk was thermized for 10 seconds at 63°C and the thermized skimmed milk was passed into a standardization tank which was kept at 6 °C. The centrifuge sludge obtained from the cream separator was combined with the single bactofugate stream obtained by combining bactofugates 1 and 2 (see below).

Another part of the same raw milk was subjected to a bactofugation treatment at 56 °C, thus also yielding a bactofugate (bactofugate 2) and a treated full fat milk. The treated full fat milk was thermized for 10 seconds at 63 °C and the thermized full fat milk stream was dosed into the same standardization tank together with the sterilized mix stream (as described below), so that the fat content of the standardized cheese milk in the standardization tank was 1.08 times higher than the protein mass concentration of the cheese milk to prepare the cheese milk of a 48+ Gouda cheese type. Cheese milk recipe and cheese milk composition are indicated in Table 3 and Table 4, respectively.

Table 3 - Cheese milk recipe

Table 4 - Cheese milk composition 0

0 as determined by Foss Milkoscan FT2 (IR)

Bactofugates 1 and 2 were combined into a single bactofugate stream.

This bactofugate stream was passed into a cooled buffer tank (6 °C). The composition of the combined bactofugate stream present in the cooled buffer tank is indicated in Table 5.

The standardized cheese milk was meanwhile pasteurized for 15 seconds at 75 °C, the pasteurized cheese milk thus obtained was cooled and then passed into a cheese vat for coagulation. Starter culture, colorant, calcium chloride and coagulant were added and a curd was allowed to form at 32 °C during 21 minutes. The curd was subsequently cut, so that whey was released from the gel network. The whey was removed through a sieve by suction and contained curd fines of up to 1 mm in diameter (first whey). After the first whey was removed from the cut curd, warm washing water was added to the remaining curd mass under continuous stirring so that the temperature of the curd mass in the cheese vat increased to approximately 35 °C. Stirring continued for 9 minutes. The curd mass was subsequently pumped into a buffer tank from it was passed into a draining column where further whey was drained from the curd mass (second whey). This second whey was combined with the first whey into a single whey stream. This whey stream was then cleaned by passing it through a whey clarification centrifuge operated at approximately 34 °C, resulting in a clarified whey and a whey stream comprising curd fines. This whey stream comprising curd fines having a temperature of approximately 34 °C was passed into a two-stage homogenizer, where the curd fines were homogenized at successively 350 bar and 50 bar resulting in a stable processed curd fines suspension with a particle size distribution (as determined by laser diffraction using a Malvern Mastersizer 2000) of 98 vol% < 146 pm and 95 vol% < 117 pm.

The processed curd fines stream was subsequently passed into a cooled buffer tank specifically intended to contain processed curd fines and whey cream.

The clarified whey obtained from the whey clarification centrifuge was fed into a whey decreaming centrifuge operated at approximately 34 °C, resulting in whey cream and defatted clarified whey. The whey cream was subsequently passed into the same cooled buffer tank as the processed curd fines stream. The composition of the mix of whey cream and processed curd fines present in the cooled buffer tank is indicated in Table 5. Table 5 - Composition of recycle streams

After sufficient material was collected in the bactofugate buffer tank, the bactofugate was fed to the multitube sterilizer, where it was sterilized by keeping the stream at 90 °C for 2 minutes followed by 125 °C for 15 seconds. The sterilized bactofugate stream was subsequently rapidly cooled to 7 °C and fed into a dosing tank kept at 6 °C. From this dosing tank the sterilized bactofugate was fed to the standardization tank referred to above, from which the standardized cheese milk was further processed as described above.

After sufficient material was collected in the buffer tank containing the whey cream and processed curd fines, the whey cream and processed curd fines mixture was fed into the multitube sterilizer, where it was sterilized by keeping the mix stream at 90 °C for 2 minutes followed by 125 °C for 15 seconds. This sterilized mix stream was subsequently rapidly cooled to 7 °C and fed into a dosing tank kept at 6 °C. From this dosing tank the sterilized mix was fed to the standardization tank referred to above, from which the standardized cheese milk was further processed as described above.

After removal of the second whey the curd leaving the draining column at the bottom is cut and the resulting cylindrically shaped curd blocks are put into round pressing vats in which they are pressed into wheel-shaped cheeses of 12,5 kg. These cheeses were subsequently further processed into the final cheese product by brining, coating and ripening the cheese.

By using this process it was found that bactofugate, curd fines and whey cream, in this case also supplemented with centrifuge sludge from the cream separator, could be effectively recycled, thereby optimizing the use of these streams in producing cheese. Example 3 - Preparation of Emmenthaler 45+ cheese

Raw milk was heated to 55 °C and subjected to a fat separation treatment in a cream separator. The resulting skimmed milk was subjected to a bactofugation treatment at 55 °C by two centrifuges in series, thus yielding a bactofugate (bactofugate 1) and treated skimmed milk. The treated skimmed milk was thermized for 12 seconds at 67.5 °C and the thermized skimmed milk was passed into a storage tank which was kept at 6 °C.

Another part of the same raw milk was subjected to a bactofugation treatment at 55 °C by two centrifuges in series, thus also yielding a bactofugate (bactofugate 2) and a treated full fat milk. The treated full fat milk was thermized for 12 seconds at 63 °C and the thermized full fat milk stream was passed into a storage tank for thermized full fat milk and the sterilized mix stream (as described below) which was kept at 6 °C.

Bactofugates 1 and 2 were combined into a single bactofugate stream. This bactofugate stream was passed into a circular pipeline which was continuously kept at 75 °C.

The calculated streams from the different storage tanks to arrive at the cheese milk recipe indicated in Table 4 (fat/protein ratio of 0.85 w/w) were sequentially fed to the pasteurizer and pasteurized for 15 seconds at 72 °C. The pasteurized streams thus obtained were cooled to the coagulation temperature and then passed into a cheese vat to prepare the curd of a 45+ Emmenthaler cheese. Cheese milk recipe and cheese milk composition are indicated in Table 6 and Table 7, respectively.

Table 6 - Cheese milk recipe Retentate is obtained in the preparation of micellar casein isolate and has a dry matter content of 16.3 wt%, a fat content of 0.2 wt%, a lactose content of 4.2 wt% and a total protein content of 10.5 wt%. Retentate is stored at 6 °C.

Table 7 - Cheese milk composition ^x > as determined by Foss Milkoscan FT2 (IR)

Starter culture, calcium chloride were added to the cheese vat and a curd was allowed to form at 29 °C during 25 minutes. The curd was subsequently cut, so that whey was released from the gel network. The whey was removed through a sieve by suction and contained curd fines of up to 1 mm in diameter (first whey). After the first whey was removed from the cut curd, warm washing water was added to the remaining curd mass under continuous stirring so that the temperature of the curd mass in the cheese vat increased to approximately 36 °C. A second amount of whey was removed (second whey) and, subsequently, a second amount of warm washing water was added to the remaining curd mass under continuous stirring so that the temperature of the curd mass in the cheese vat increased to approximately 38 °C. Stirring continued for 13 minutes. The curd mass was subsequently pumped into a buffer tank from it was passed into a draining column where further whey was drained from the curd mass (third whey). This third whey was combined with the first and second whey into a single whey stream. This whey stream was then cleaned by passing it through a whey clarification centrifuge operated at approximately 34 °C, resulting in a clarified whey and a whey stream comprising curd fines. This whey stream comprising curd fines (further: curd fines stream) having a temperature of approximately 34 °C was passed into a tank. Additional, 4 wt% (IM) of sodium hydroxide solution was fed to this tank to adjust the pH of the curd fines stream to 7.0. The tank is equipped with a mixing impellor and an inline pH probe that measures the pH of the mixture of curd fines stream and added sodium hydroxide solution. The dosing of the sodium hydroxide solution was controlled by a proportional-integral-derivative (PID) controller to keep the pH at the setpoint of 7.0. The weight ratio of sodium hydroxide solution flow to curd fines stream was 1.2:100. The curd fines stream with adjusted pH was fed to a two-stage homogenizer, where the curd fines stream was homogenized at successively 350 bar and 50 bar resulting in a stable processed curd fines suspension with a particle size distribution (as determined by laser diffraction using a Malvern Mastersizer 2000) of 98 vol% < 195 pm and 95 vol% < 147 pm with a mean particle size of 62 pm.

The processed curd fines stream was subsequently passed into the same circular pipeline as the bactofugate.

The clarified whey obtained from the whey clarification centrifuge was fed into a whey decreaming centrifuge operated at approximately 34 °C, resulting in whey cream and defatted clarified whey. The whey cream was subsequently passed into the same circular pipeline as the bactofugate and processed curd fines stream.

Bactofugate, processed curd fines and whey cream were, accordingly, dosed into the circular pipeline that was kept at 75 °C. The resulting circular mix stream had a pH of 6.7 and was passed into a continuously stirred, hot tank which was also kept at 75 °C. It took 5 hours to completely fill the hot tank. After filling the temperature of the tank was increased to 95 °C and the mixture was sterilized for 40 minutes at 95 °C. The sterilized mix stream was subsequently rapidly cooled to 6 °C by a heat exchanger and was fed to the storage tank referred to above (i.e. storage tank containing thermized full fat milk and sterilized mix stream). Composition of the sterilized mix stream is indicated in Table 8.

Table 8 - Composition of sterilized mix stream. After removal of the third whey the curd leaving the draining column at the bottom is cut and the resulting curd cylindrically shaped blocks are put into round pressing vats in which they are pressed into euroblock-shaped cheeses of 15 kg. The cheeses were subsequently further processed into the final cheese product by brining, packaging the euroblock-shaped cheese in foil and ripening the cheese.

By using this process it was found that bactofugate, curd fines and whey cream could be effectively recycled, thereby optimizing the use of these streams in producing 45+ Emmenthaler cheese.

Example 4 - Heat stability testing

The effects of pH, casein concentration and temperature on the heat stability of casein was tested via a standardized method (Reference: D. T. Davies and J. C. D. White, The stability of milk protein to heat, J. Dairy Res. 33 (1966), p 67-81). Testing was carried out with bactofugate, whey cream and processed curd fines suspension of Example 3 as pure raw materials and a regular mixture of these raw materials (45 wt% whey cream, 28 wt% processed curd fines suspension, 12 wt% bactofugate, 15 wt% potable water). The pure components were used to prepare samples with casein concentrations lower and higher compared to the regular mixture.

Samples were prepared as follows: the pure raw materials were inactivated by a 5 min heat treatment at 75 °C to inactivate the chymosin prior to mixing. Sodium azide was added to the samples (0.02m%) to prevent spoilage of the sample after heating. Subsequently, two samples were prepared: Sample A (low in casein content) and sample B (high in casein content). The recipe of the two samples is given in Table 9.

Table 9 - Composition of samples Three sample portions were taken of each of Sample A and Sample B. The pH of these portions was adjusted by adding a 1 M sodium hydroxide to increase the pH or 1 M hydrochloric acid to lower the pH, to create two pH series with the following pH, 6.3, 6.5 and 6.7, respectively. In the next step the samples were incubated at 75 °C for three hours. Of the incubated samples the heat stability was determined in duplo at 102.5 °C, 105 °C and 107.5 °C. The heat coagulation time of the samples was determined in a thermostatically controlled oil bath. Samples (~1.2 ml) were placed in thin-walled glass tubes, which were placed in a rack. The rack was placed in the oil bath and gently oscillated at 6 min ¹ . The time from placing the tubes in the rack until the first visible signs of coagulation observed, was noted as the heat coagulation time (HOT). The chosen temperatures to determine the HCT were chosen slightly lower than the typical sterilization temperatures to allow sufficient time to follow the coagulation point and measure differences better. In general, at a lower temperature the coagulation will go slower, but will give a good indication at the higher sterilization temperatures.

The composition of the mixed samples after pH adjustment is given in Table 10. The protein content of Sample B is almost two times higher than Sample A.

Table 10 - Composition of samples

The results of the HCT tests are given in Table 11. The following trends are visible in respect of the HCT:

• HCT decreases slightly with increasing temperature • HCT decreases strongly with decreasing pH of the samples

• Bactofugate-rich product is more stable at pH 6.7, despite ~2-fold higher protein content

Table 11 - Results of HCT test

As can be seen from Table 11: if the pH of the samples was lower than 6.5, very low heat stability of samples was observed, regardless of the proportions of the different streams in the product. The main source for a low pH of samples was found to be the curd fines suspension, for which pH values as low as 5.4 have been observed. In contrast, whey cream and bactofugate were typically found to have pH values higher than 6.6. Hence, it is important to control pH of the different recycle streams and in particular of the curd fines suspension, as this stream has the lowest pH and could cause a low pH of the recycle mix stream if the three recycle streams are mixed into a single recycle stream. Such pH control and, if necessary, adjustment of the pH of particularly the curd fines suspension to a safe value of at least 6.5 is an essential requirement for assuring a sufficiently high heat stability of recycle streams, so that fouling can be minimized.

For ensuring sufficient thermal stability of the mixture, efficient control of pH is necessary to prevent heat induced coagulation of the casein present. The pH should not be lower than 6.5, primarily control of the pH of the curd fines fraction is crucial.